downunder

[link=http://www.modeltechnics.com/glowplug/firepower.html]Here's[/link] a very good read about glow plugs and near the bottom are the results of tests done on various engines using 6 different heat range plugs (plus a competitor's plug although they don't give a brand name). Basically what it boils down to is that the best plug is the one giving the highest revs but giving some consideration to how well the engine idles and transitions. There's no "one plug suits all" because so much depends on the type of engine, fuel used, prop etc but it's not as bad as it might seem because it's only when you go to an extreme with plug heat range that you might see any problem. For general sport use with sensible nitro amounts then there's a fairly large range of plugs that will be quite suitable. That's more or less why the OS #8 plug is usually recommended because it's in the middle of the acceptable range.